Powdered epoxy coating compositions have many applications. One useful application is in the field of motors. A typical motor can contain many components, e.g., a rotor (or armature) and a stator. It is very common for the rotor and the stator to contain wires, typically copper wires, wound about a part. The wound wires are commonly referred to as a “winding”. Motor or coil windings require an insulating coating, over the metal windings, to protect the windings from dust, moisture, and chemicals. In some cases the insulating materials tend to be porous and moisture absorbent. Motors having windings with inadequate protection, due to an inferior or damaged coating, could cause equipment failure when exposed to adverse conditions such as high humidity environments. Materials drawn into motor windings during normal use may produce a moisture absorbing buildup that impairs motor ventilation. Moisture drawn into motor windings in this manner creates paths of current flow to ground. Once this path is developed the carbon trail left behind will continue to conduct until failure occurs.
Epoxy coatings have been shown to protect metal windings. For example, U.S. Pat. No. 5,747,565 (Ono et al.) discloses an epoxy powder coating composition suitable for use in insulating electric and electronic parts. The patent discloses a composition comprising (A) 100 parts by weight of a mixed epoxy resin having an epoxy equivalent of 800-2000 and including (i) a diglycidyl ether of bisphenol A having an epoxy equivalent of 180-2500 and (ii) a rubber modified epoxy resin having an epoxy equivalent of 180-2500 and obtained by reaction of a diglycidyl ether of bisphenol A with a carboxyl terminated acrylonitrile butadiene copolymer; (B) a mixed curing agent consisting of (i) 0.05 parts by weight of an imidazole compound, (ii) 0.5-10 parts by weight of dicyanodiamide and (iii) 1-10 parts by weight of a dihydrazide of a dibasic carboxylic acid and (C) 50-100 parts by weight of silica.
Japan Kokai 11-172075 discloses an epoxy resin composition comprising (A) at least 60 wt % of a cystalline epoxy resin, (B) a phenolic resin curing agent which can be a Bisphenol A type epoxy, (C) a fused silica powder and (D) at least one type of hardener accelerator such as an imidazole.
Japan Kokai 07-258384 discloses an epoxy resin composition comprising (A) crystalline epoxy resin, (B) a phenolic resin curing agent of a bisphenol A epoxy resin type, (C) a novolak phenolic resin, (D) Bisphenol A, and (E) an imidazole accelerator.
It is known in the art to also use a liquid varnish to coat the windings. A typical process involves trickling the varnish on the winding to coat the metal wires. Such a process tends to be time consuming. Also, varnishes typically contain volatile organic components making them environmentally unfriendly.
While the foregoing technologies may be useful, what is needed in the art is different powdered epoxy compositions that exhibit good adhesion and yet provide good flow characteristics when the composition is applied to a variety of substrates, particularly metal substrates.